1. Field of the Invention
The invention relates broadly to methods and devices for selective control of valves or other downhole devices. In one particular aspect, the invention provides a signal indicating an opportunity for altering the operational mode of the downhole device. Further, the invention relates to means for remotely altering the operational mode of a component within a well bore.
2. Description of the Related Art
A number of hydraulic tools, such as a borehole underreamer, a section mill and so forth, function by extending and retracting, through manipulation of hydraulic pressure, cutter blades from the interior of a body of the underreamer to selectively ream a portion of a borehole. A means is required to extend or retract the moveable blades of the underreamer as it is operated in the borehole.
An early method to perform, for example, underreaming operations required the drill string to be tripped out of the borehole, other tools removed from the string, and the underreamer attached to the drill string. The whole assembly was then tripped back into the borehole. Increasing fluid pressure within the drill string then extended the underreamer blades. After the underreaming operation was completed, the procedure was reversed to remove the underreamer from the drill string. One disadvantage to this method is that no other tools, such as a drill bit assembly, MWD assembly, adjustable stabilizers, or the like, can be operated without also operating the underreamer. Obviously, this procedure is also costly, especially if the depth of the borehole is in the thousands of feet.
Another, more cost effective method, attaches a hydraulically actuatable underreamer to a drill string and when a desired depth is reached for commencement of the underreaming operation, a plug or "dart" is retrieved by wireline through the interior of the drill string to allow differential pressure to actuate the underreamer. When the underreamer operation is completed, the dart can be dropped back into the borehole to deactivate the tool. Hydraulic pressure can no longer open the underreamer.
Again, the method of controlling the tool is costly since the drilling operation is interrupted when the dart is moved in and out of the borehole. Moreover, in other hydraulically actuatable tools that are indexed to alternate positions by manipulation of flow, the tool generally has to be reset to the desired position each time hydraulic circulation is interrupted.
Still another method to control hydraulic actuatable tools such as anchors, valves, packers or underreamers is the use of shear pins designed to shear under specific hydraulic pressure loads to cause the aforementioned tools to perform in a predetermined manner and perform a specific function. These systems are disadvantaged in that they are one time mechanisms. Once the pins are sheared, the tool cannot be reset. The presence of debris within the borehole or sudden impacts to these tools may index or even weaken or shear triggering devices prematurely.
An example of an apparatus and method for orienting and setting a hydraulically-actuatable tool in a borehole is taught in U.S. Pat. No. 5,443,129. The patent is assigned to the same assignee as the present application and incorporated herein, by reference. The method of setting a hydraulically-actuatable tool and commencing drilling in a single trip of the drill string includes the steps of running the hydraulically-actuatable tool into the borehole on a drill string which includes an MWD (measurement while drilling) subassembly. The MWD subassembly senses the orientation of the hydraulically-actuatable tool, orients the drill string to the desired position and sets the hydraulically-actuatable tool. The tool is set by increasing the hydraulic pressure within a bypass valve positioned below the MWD subassembly to a predetermined level that will shear a shear pin in the bypass valve which allows a piston retained within the valve body to close off flow bypass ports and to direct the increased hydraulic pressure to activate the tool (for example an anchor-packer assembly) downstream of the valve.
Other hydraulically-actuatable tools utilize a combination of downhole MWD and microprocessor telemetering systems to manipulate the tools such that the tools perform in a predictable or programmed manner dependent upon conditions encountered downhole while drilling. U.S. Pat. Nos. 5,318,137, 5,318,138 and 5,332,048 relate to a method and apparatus for adjusting the position of stabilizer cutter blades utilizing the aforementioned telemetering systems. These systems are complex and rely on the workability and accuracy of MWD and microprocessing apparatus for communicating the information up the drill string to the data processing equipment at or near the borehole platform, a sometimes troublesome process. Microprocessor-based tools are also expensive.
U.S. Pat. No. 5,518,073 teaches a mechanical lockout for pressure responsive downhole tools. A tester ball valve may be opened or closed upon reaching a desired borehole depth and after a packer assembly is set below the valve. The tester valve is actuated by increasing the well annulus pressure to a level above hydrostatic pressure to move a power piston associated with the valve, thus moving the ball valve from a closed position to an open position. During operation, well annulus pressure can be cycled between hydrostatic pressure and a higher pressure level to open or close the tester valve. The valve uses hydraulic fluid such as oil to drive a valve actuating piston when the annulus pressure exceeds hydrostatic pressure in combination with nitrogen under pressure to return the piston to an initial position when the annulus pressure is reduced. Alternatively, the valve may be opened or closed by increasing annulus pressure in two different stages, the second stage requiring the annulus pressure to be considerably higher than the first stage.
In order for the tester valve to function, a packer assembly must first be actuated to seal off the borehole downstream of the valve so that the annulus pressure can be increased sufficiently to cause the valve to cycle either open or closed. Moreover, if it is desired to insert the tester valve in a closed position, sliding valve actuating members must be locked together for the valve to cycle properly from the closed position to the opened position. Once the members are locked together, they cannot be separated. Further, the apparatus of U.S. Pat. No. 5,518,073 requires multiple levels of positive pressure to be applied downhole. It cannot be used by merely turning surface-based pumps on and off.
The present invention overcomes the deficiencies in the prior art.